Patent Document 1 discloses, with respect to a procedure for engaging and disengaging a wet-type frictional clutch provided in the power transmitting system of a vehicle by changing the pressure of a working fluid supplied to the clutch depending on the duty pulse output from an electronic control unit, a technology for engaging the clutch from a disengaged state by initially outputting from the electronic control unit a predetermined starting duty ratio with which to engage the clutch to a large extent until it starts to connect driving and driven members, and thereafter outputting from the electronic control unit a predetermined gradually engaging duty ratio with which to gradually engage the clutch, in every given period of time.